1. Technical Field
The present application relates to a single-panel image capture device that obtains a color image and also relates to an image processor that achieves high resolution. More particularly, the embodiments of the present invention relates to an image capture device that changes resolution and exposure time on a color component basis and to an image processor that generates a high-resolution, high-frame-rate and high-sensitivity output image based on the output image of the image capture device.
2. Description of the Related Art
According to a known technique for achieving a high resolution for a color moving picture, R, G and B color components are captured as respective input images in mutually different resolutions, exposure times and frame rates (see Patent Documents Nos. 1 and 2). In capturing such a high-resolution and high-frame-rate moving picture, however, the quantity of light incident on each pixel often runs short, thus causing a decrease in the SNR of the moving picture. Specifically, according to the technique disclosed in Patent Documents Nos. 1 and 2, as for a certain color component, an image is captured at a low resolution and a high frame rate, thereby obtaining an image with a sufficient quantity of light secured spatially. Meanwhile, as for another color component, an image is captured at a high resolution and a low frame rate, thereby obtaining an image with a sufficient quantity of light secured temporally. And based on these images (i.e., input images), the high-resolution and high-frame-rate moving picture has its resolution further increased.
Such input images can be obtained by setting the resolutions of three-panel image sensors, which capture the respective color components, to be different from each other. Alternatively, such input images can also be obtained by a single-panel image sensor. In that case, low-resolution color component images are generated by adding together signals provided by adjacent pixels.
A single-panel color image sensor with the ability to add together pixel signals on an image capturing plane is disclosed in Non-Patent Document No. 1 and Patent Document No. 3. Non-Patent Document No. 1 discloses a CMOS image sensor that can make addition on adjacent pixels. Addition can be made on vertical pixels by supplying a column select pulse to columns of horizontal pixels to be added together at the same time.
FIG. 32 illustrates an exemplary configuration for a pixel peripheral circuit in the related art and FIG. 33 shows an example of a drive timing chart.
Suppose a situation where two vertically adjacent R (red) and B (blue) pixels need to be added together. As shown in FIG. 33, an R and B pixel read signal TRANRBn on an nth row of columns of horizontal pixels (i.e., on the nth scan line) and an R and B pixel read signal TRANRBn+1 on an (n+1)th scan line are raised to H level at the same time. Then, those pixel signals are read out to an output signal line at the same time and then mixed together on the output signal line. In 1H (one horizontal scanning period) after that, a read signal is supplied to R and B pixels on the next two scan lines (i.e., (n+2)th and (n+3)th scan lines) and addition is made in the same way. Horizontal pixels can be added together by providing a binning circuit. A CMOS image sensor converts signal charge that has been stored in pixels into an electrical signal such as a voltage and then outputs the electrical signal to an external device outside of the image sensor. That is why the CMOS image sensor can transmit a signal rapidly and can speed up the read operation.
Patent Document No. 3 proposes a color CCD single-panel image sensor that can get pixel addition done on an image capturing plane. In making a vertical pixel addition, the image sensor disclosed in Patent Document No. 3 supplies a signal with high voltage level to a vertical. CCD cell every number of pixels to be subjected to the addition, thereby producing a deep potential well. In such a state, a vertical transfer is made with respect to multiple pixels to store electric charge, corresponding to the number of pixels, in the potential well. By mixing together electric charge supplied from multiple pixels in the potential well of a single semiconductor surface, the vertical pixel addition can get done. Likewise, horizontal pixel addition can also get done by forming a deep potential well and making a horizontal transfer for the number of pixels to be subjected to the addition. The CMOS image sensor makes the pixel addition after having transformed the pixel charge into an electrical signal. That is why noise to be inevitably produced when the charge is transformed into a voltage is superposed on each of the signals to be added together. For example, when addition is going to be made on four pixels, charge-voltage transformation noise will be accumulated for those four pixels. On the other hand, a CCD image sensor makes a pixel addition by adding together the pixel charge itself and then performing the charge-voltage transformation. The noise to be involved with this transformation will be superposed for only one pixel, no matter how many pixels need to be added together. That is why this technique is advantageous in terms of the SNR of the pixel signals obtained by making the addition.
Patent Document No. 4 and Non-Patent Document No. 2 disclose a technique for adding together signals on output signal lines in a charge-coupled device in a horizontal transfer section.